Germline stem cells (GSCs) are defined by their dual capacity for both self-renewal and the generation of a continuous supply of gametes through differentiation. A complex regulatory network including signaling pathways, cell cycle regulation, and gene expressional regulation, controls the balance between self-renewal and differentiation. Moreover, aberrant regulation of this network can result in either loss of GSCs or uncontrolled germ cell proliferation, leading to germline tumors. Although significant progress has been made in dissecting the molecular mechanisms of each type of regulation, the mechanisms by which these controls are linked during germline development and tumorigenesis remain a major challenge. The proposed experiments address two fundamental molecular controls of germline development. First, how do extrinsic signaling pathways establish a balance of germline proliferation and differentiation? Second, how do intrinsic regulators maintain this balance in the germline. Specifically, we focus on GLP-1/Notch signaling-mediated germline proliferation using the nematode Caenorhabditis elegans as a model system. The C. elegans germline has provided a framework for educational and scientific research resources because of the simplicity of the worm, its well-characterized genetic background, and powerful experimental tools. Although C. elegans is primitive and small, it shares many fundamental molecular and cellular regulatory mechanisms with more advanced organisms, including humans. Using a combination of bioinformatics, genetics, cell biology, and biochemical approaches, we have identified several regulators that regulate GLP-1/Notch-mediated germline proliferation. Those include RNA regulators (i.e., PUF-8, GLD-1, GLD-2) and cell cycle regulators (i.e., CYB-3, CDK-1, CDC-25.1, and WEE-1.3). Based on our preliminary results, we hypothesize that the PUF-8 and WEE-1.3 proteins may inhibit GLP-1/Notch-mediated germline proliferation by inhibiting CYB- 3/CDK-1 activity as well as PUF-8 may promote GLP-1/Notch-mediated germline proliferation by inhibiting GLD-1/GLD-2 expression. These results speculate that PUF-8 may act a key regulator to control the balance between proliferation and differentiation in the C. elegans germline. Indeed, all regulators we propose to investigate are broadly conserved and expressed in vertebrate and invertebrate germlines. We therefore suggest that similar molecular circuitry may control germline development in other organisms, including humans.